In order to form a successful compression joint using a compression sleeve, one of the major considerations is that the crimping tool shall not scuff, cut, scrape or gouge the compression sleeve during the crimping operation.
Further, it is essential that the crimping jaws approach each other in end-to-end parallelism. If the jaws do not engage each other in end-to-end parallelism, then, there is a probability of pinching and cutting of the compression sleeve at one point around the circumference thereof, while other points on the circumference of the compression sleeve are not fully compressed.
This can result in a faulty joint, in that blow-out and leakage can occur at the damaged portion of the compression sleeve when the pipe line is subjected to pressure, and, in the alternative, leakage axially of the pipe can occur at the insufficiently compressed portions of the compression sleeve
For this reason, crimping tools for use in assembling compression couplings are required to include crimping jaws that can move radially with respect to the longitudinal axis of the compression sleeve.
However, a simple pliers type linkage cannot successfully accomplish that movement in that the jaws of the pliers are each moving on an arcuate path. The result is that considerably more force is exerted on the compression sleeve on its radius closest to the pivot of the pliers, with a danger of cutting of the compression sleeve at that radius, while at the same time lesser and possibly insufficient compressive force is exerted at the diametrically opposite radius.
For this reason, it was proposed in German patent 3,423,283 published Jan. 2, 1986 to provide a crimping tool in which opposite jaws of the crimping tool are moved in parallelism with each other when progressing from the open position of the crimping tool to the closed crimping position thereof.
In order to accomplish that movement, this prior teaching requires the crimping jaws to be positionally held by rollers attached to the respective jaws, and which are moved along cam tracks in a support plate during their movement between the opened and closed positions of the jaws. Further, the jaws are required to ride on ramp cams, which further act to guide the jaws in parallelism with each other during a closing movement of the jaws.
Crimping tools of this type encounter extremely high working pressures when in use. This in turn results in rapid wear of the rollers and their associated journals, and in turn, results in rapid wear of the ramp cams, and further in turn results in the jaws being free to approach each other other than in true parallelism, due to play in the mechanism.
These problems are further exaggerated due to the fact that the rollers engage their cam tracks in line engagement only, and also, the jaws engage their ramp cams in line engagement only.
In the event that there is play in the mechanism, and the crimping jaws approach the compression sleeve other than in parallelism with each other, then, gouging and scuffing and possible cutting of the compression sleeve will result, and also, the compression sleeve can be compressed off-center with respect to its longitudinal axis, this resulting in over compression of the O-rings at one radius of the compression sleeve and possible destruction of the O-ring at that location, and a diametrically opposite insufficient compression of the O-ring resulting in leakage axially of the pipe at that location.
In order to eliminate these disadvantages in the prior art crimping tool of German patent 3,423,283, it is proposed in U.S. Pat. No. 5,148,698 issued Sep. 22, 1992 to provide a crimping tool having three crimping jaws, one of which is fixed relative to the frame of the crimping tool, and, the other two of which can slide within the supporting arm of those jaws, in this manner to produce a crimping force that approximates a truly radial compression on the compression sleeve.
This U.S. patent teaches that the three dies move in a radial fashion when crimping a fitting. In practice, for that to happen, a multitude of factors have to be taken into consideration, with at least one of those factors being beyond the control of the jaw manufacturer.
In order to produce a truly radial motion of the jaws, the friction between the dies and the fitting must be within a very narrow range. If it is not within that range, the pre-loaded springs that are used to initially position the two moving dies, will not be at the right pre-load pressure to compensate for the friction loads. In practice, the friction imposed on the jaws can vary to a large extent, the result being that in practice the dies do not always come together in a truly radial path, this resulting in a non-uniform crimp.
When this happens, the pipes that are being joined to fittings do not always stay in axial alignment with the fittings. This is because of angular deflection between the pipe and the fittings caused by a non-uniform crimp geometry due to the dies moving in a non-uniform manner. Non-uniformity of the crimp can result in severe fitting pinching at the die corners, and, failure of the dies to close fully.
Additionally, dirt builds up between the respective die segments, which requires cleaning of the dies as an every day occurrence. If dirt is present between the dies as they come together, the dirt prevents full closure of the dies, this resulting in an incomplete crimp. This problem is compounded according to the teachings of U.S. Pat. No. 5,148,698, in that dirt readily accumulates at the juxtaposed faces of the fixed die and the movable dies, the positioning of those juxtaposed faces making the crevice between the juxtaposed faces hard to access and to clean.
Further, the three-jaw design of the prior art severely limits how far the jaws can be opened, this in turn requiring the crimping tool to be fit over the pipe and then slid axially of the pipe and over the fitting before a crimping operation can be effected.
The use of one fixed and two movable compression jaws results in three points around the circumference of the compression ring that can be subjected to possible pinching and gouging of the compression sleeve at those points.
Further, the compression tool itself is of complex construction and expensive to manufacture.
Further, while it is expected that the durability of the tool will be greater than that described in German patent 3,423,283, it is subject to wear on the sliding faces of the two movable jaws, which, owing to the requirement for one fixed and two sliding jaws, must be of reduced sliding contact area with their supporting arm.